通常我们会有这样的需求,即停止一个线程。在java的api中有stop、suspend等方法可以达到目的,但由于这些方法在使用上存在不安全性,会带来不好的副作用,不建议被使用。具体原因可以参考Why is Thread.stop deprecated。
Thread.stop
在本文中,将讨论中断在java中的使用。
中断在java中主要有3个方法,interrupt(),isInterrupted()和interrupted()。
接下来,看看具体在代码中如何使用。
interrupt()不能中断在运行中的线程,它只能改变中断状态而已。
public class InterruptionInJava implements Runnable{ public static void main(String[] args) throws InterruptedException { Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava"); //start thread testThread.start(); Thread.sleep(1000); //interrupt thread **testThread.interrupt();** System.out.println("main end"); } @Override public void run() { while(true){ if(Thread.currentThread().isInterrupted()){ System.out.println("Yes,I am interruted,but I am still running"); }else{ System.out.println("not yet interrupted"); } } } }
结果显示,被中断后,仍旧运行,不停打印Yes,I am interruted,but I am still running
那么,如何正确中断?
既然是只能修改中断状态,那么我们应该针对中断状态做些什么。
public class InterruptionInJava implements Runnable{ public static void main(String[] args) throws InterruptedException { Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava"); //start thread testThread.start(); // Thread.sleep(1000); //interrupt thread testThread.interrupt(); System.out.println("main end"); } @Override public void run() { while(true){ if(Thread.currentThread().isInterrupted()){ System.out.println("Yes,I am interruted,but I am still running"); **return;** }else{ System.out.println("not yet interrupted"); } } } }
修改代码,在状态判断中如上,添加一个return就okay了。 但现实中,我们可能需要做的更通用,不禁又要发出天问,如何中断线程?答案是添加一个开关 。
public class InterruptionInJava implements Runnable{ private volatile static boolean on = false; public static void main(String[] args) throws InterruptedException { Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava"); //start thread testThread.start(); Thread.sleep(1000); **InterruptionInJava.on = true;** System.out.println("main end"); } @Override public void run() { while(!on){ if(Thread.currentThread().isInterrupted()){ System.out.println("Yes,I am interruted,but I am still running"); }else{ System.out.println("not yet interrupted"); } } } }
会输出类似结果,这表明是成功中断了的:
这种开关的方式看起来包治百病,但是当遇到线程阻塞时,就会很无奈了,正如下面代码所示:
public class InterruptionInJava implements Runnable{ private volatile static boolean on = false; public static void main(String[] args) throws InterruptedException { Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava"); //start thread testThread.start(); Thread.sleep(1000); InterruptionInJava.on = true; System.out.println("main end"); } @Override public void run() { while(!on){ try { Thread.sleep(10000000); } catch (InterruptedException e) { System.out.println("caught exception: "+e); } } } }
线程被阻塞无法被中断。这时候救世主interrupt函数又回来了,它可以迅速中断被阻塞的线程,抛出一个InterruptedException,把线程从阻塞状态中解救出来,show the code。
public class InterruptionInJava implements Runnable{ private volatile static boolean on = false; public static void main(String[] args) throws InterruptedException { Thread testThread = new Thread(new InterruptionInJava(),"InterruptionInJava"); //start thread testThread.start(); Thread.sleep(1000); **InterruptionInJava.on = true; testThread.interrupt();** System.out.println("main end"); } @Override public void run() { while(!on){ try { Thread.sleep(10000000); } catch (InterruptedException e) { System.out.println("caught exception right now: "+e); } } } }
结果截图,达到预期。
这种情形同样适用io阻塞,通常io阻塞会立即抛出一个SocketException,类似于上面说的InterruptedException。
原文链接:https://www.cnblogs.com/jenkov/p/juc_interrupt.html